The present invention relates to a silicate containing adhesive composition and process for producing the same.
Silicate containing adhesives have been widely used in the paper industry for the manufacture of laminated products such as corrogated board, paper tubes, paper cones and the like. Silicate adhesives are desirable for these uses because of their relatively low cost, ease of preparation and the strong adhesive bond they produce.
A variety of silicate containing adhesives have been disclosed in which a vegetable protein material is added to increase the shelf life or adhesive characteristics of the composition. U.S. Pat. No. 2,457,108 describes the preparation of a silicate adhesive which includes a vegetable protein flour in an amount of 2 to 50% to provide an increased shelf life for the silicate adhesive composition without a corresponding reduction in adhesiveness. U.S. Pat. No. 2,681,290 also describes a silicate containing adhesive composition wherein a vegetable protein-carbohydrate flour is employed and it is preferred that the flour have a starch level of greater than 15% by weight since this improves the working life and viscosity of the adhesive composition. Both of these compositions, however, require the application of heat in order to provide the necessary viscosity for adherence to the surfaces to be joined and finally to form the necessary bond between the two surfaces to be joined. Thus, while being acceptable for most applications, it would be preferred if a silicate adhesive composition having cold setting characteristics and higher viscosity at ambient temperatures could be developed since this would avoid the use of heat which is not always desirable in the manufacture of laminated paper products.
U.S. Pat. No. 2,894,847 describes a cold setting silicate adhesive composition which contains a soy insolate for thickening of the silicate composition and to provide the necessary adhesiveness. While the use of an isolate does provide an improvement in the properties of the silicate adhesive composition, nevertheless, somewhat lower silicate levels in the adhesive composition must be employed since the isolate will otherwise precipitate or not be capable of dispersion when a high level of silicate is used. Furthermore, such a composition requires a substantial percentage of isolate in order to provide the necessary solids level in the adhesive composition so that the composition will have the necessary viscosity and tack for application to the surfaces to be joined together.
The use of various types of cellulosic compounds as thickeners for silicate adhesives has also been proposed. U.S. Pat. No. 3,241,990 describes the use of cellulosic fibrous material such as wood pulp to control the viscosity of silicate solutions used in the formation of solid silaceous articles. Impregnating compositions to improve water resistance have also been proposed which comprise silicate solutions containing carbohydrates such as starch or cellulose derivatives.
In spite of the variety of approaches that have been used for the formation of silicate compositions, there is still a need for a cold setting silicate adhesive composition that is suitable as a bonding agent for paper products. The continuous production of bonded paper products require an adhesive which can be easily formed and maintains its consistency for application on a continuous basis. Furthermore, the adhesive should have sufficient viscosity so that the smallest amount possible is applied to achieve adhesion thereby improving the economics of the process as well as preventing excessive penetration of the adhesive into the relatively porous surfaces of paper products.
It is therefore an object of the present invention to provide a silicate containing adhesive composition having cold setting characteristics at a low enough solids level that it may be easily applied, yet that it has a substantial viscosity at ambient temperatures thereby providing the necessary tack and adhesive strength.
It is a further object of the present invention to provide a silicate containing adhesive composition which is of relatively low cost and other desirable characteristics in the production of laminated paper products and the like.
It is another object to provide a silicate adhesive composition that maintains its consistency to permit use in a continuous laminated paper making process.
These and other objects have been achieved in the present invention.